"You can find a low-frequency, stable clock source and use it to calibrate a baud-rate generator or event timer. One source of a low-frequency, stable clock is the line voltage. This voltage is a good source 50- or 60-Hz frequency that you can easily interface to the microcontroller's 16-bit timer. By counting CPU cycles for a half cycle of the external clock, you can determine the frequency of the microcontroller's internal RC oscillator and calibrate the baud rate." Link to EDN story: http://www.devrs.com/pic/ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body